This proposed R13 application covers the 14th meeting in a long standing series of the International Workshop on Opportunistic Protists (i.e. IWOP-14). These meeting are devoted to protists that cause serious problems in patients with defective immune systems, such as those receiving immunosuppressive therapies or with immune system debilitating diseases, such as AIDS. Many of these poorly understood pathogens were initially recognized due to their increased frequency in opportunistic settings, such as in HIV/AIDS and transplantation; however, it is now appreciated that these are also pathogens of immune competent hosts. Several of these organisms, due to their transmission by food and water, are also biodefense category B pathogens and environmental protection agency (EPA) pathogens of interest. The IWOP meeting was initiated in 1988 to serve the small, but growing international scientific community interested in working with the unusual, non-cultivatable organism Pneumocystis. At the time, Pneumocystis was relatively unknown and was ignored by many in the microbiological community. There was a need for a small meeting where scientists could exchange new techniques and experiences gained from working with these fastidious organisms. A basic tenet of the IWOP Workshops is a free exchange of information facilitated by open admission to the meeting. It has and is focused on students, trainees, young investigators and under-represented scientists. The 2nd through 11th IWOP meetings grew to include other OP-based community groups that experienced many of the research challenges facing the Pneumocystis community. The IWOP meetings now include research presentations on Cryptosporidia; Microsporidia; Toxoplasma gondii; and free-living amebae that are pathogenic. In recent years, IWOP has also begun serving as a forum for researchers of other eukaryotic microbial parasites that present pathologies in immune deficient individuals distinct from that observed in immune competent patients. Today, the IWOP meetings are regarded as critical meetings for most researchers investigating the basic science of Pneumocystis, Cryptosporidia, and Microsporidia. It is the meeting at which community based projects (e.g. genome sequencing, animal models, culture techniques, etc) and consensus papers (i.e. taxonomic status, research priorities, nomenclature standards) have been developed. Because many of these organisms are not well represented in larger fungal or parasitology meetings, research progress would clearly be severely hampered if this singular forum was no longer held. In comparison to other larger meetings these Workshops provide current updates that have not yet reached the literature.